Self‐Alignment of Low‐Valent Octanuclear Palladium Atoms

Abstract

A linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)phenylphosphino]methane (dpmppm) was used to synthesize linear octapalladium-extended metal atom chains as discrete molecules of [Pd8(μ-dpmppm)4](BF4)4 (1) and [Pd8(μ-dpmppm)4L2](BF4)4 (L=2,6-xylyl isocyanide (XylNC; 2), acetonitrile (3), and N,N-dimethylformamide (dmf; 4)), which are stable in the solution states and show interesting temperature-dependent photochemical properties in the near IR region. Variable temperature NMR studies demonstrated that at higher temperature T≈140 °C the Pd8 chains were dissociated into Pd4 fragments, which were thermodynamically self-aligned to restore the Pd8 chains at lower temperature T<60 °C. The coldspray ionization mass spectra suggested a possibility for further aggregation of the linear tetrapalladium units.

Chiral Self‐Recognition between Stereogenic Tetrapalladium Units Affording Pd8 Chains Supported by Homochiral Tetraphosphines

“…Complexes 6 – 9 exhibited temperature‐dependent characteristic absorption spectral changes (Supporting Information, Figures S5–S7) as observed for the Pd 8 complexes with meso ‐dpmppm 1 – 4 . The intensities of NIR absorptions increase at low temperature at 938 nm ( 6 , −30 °C in CH 3 CN), 948 nm ( 7 , −50 °C in dmf), 946 nm ( 8 , −30 °C in CH 3 CN), and 965 nm ( 9 , −30 °C in CH 2 Cl 2 ), whereas they decrease at room temperature and disappeared at higher temperature.…”

Stepwise Expansion of Pd Chains from Binuclear Palladium(I) Complexes Supported by Tetraphosphine Ligands

“…The isolated compound was analyzed by IR, UV−vis−NIR, 1 H and 31 P{ 1 H} NMR, and ESI−MS spectroscopy. 11 To a solution of [2](PF 6 ) 2 ·CH 2 Cl 2 (101 mg, 57 μmol) in acetonitrile (7.5 mL) was added [Pd(dba) 2 ] (66 mg, 115 μmol), and the reaction mixture was heated at 60°C for 3 h. The solution was passed through a membrane filter and concentrated to ca. 5 mL.…”

“…The 1 H{ 31 P} NMR spectra of[4](PF 6 ) 4 (Figure S11b) exhibited the characteristic lower field-shifted doublets at 1.02 and 0.85 ppm, which correspond to the methylene protons of dpmppm ligands due to ring current effects of the C−H/π interactions as observed in the crystal structure of[4](BF 4 ) 4 11. The VT UV− vis−NIR spectral changes for an acetonitrile solution of[4](PF 6 ) 4 are depicted inFigure S9, featuring thermochromics behavior with an intense absorption of 896 nm at −30°C.…”

“…8c Recently, we synthesized a methylene-bridged linear tetraphosphine, meso-bis[(diphenylphosphinomethyl)-phenylphosphino]methane (dpmppm), 9,10 and have been successful in establishing low-valent octapalladium chains supported by dpmppm (Scheme 1a). 11 Reaction of the tetraphosphine with 2 equiv of [Pd(dba) 2 ] in the presence of Cu I species yielded a coordinatively unsaturated Pd 8 rod, [Pd 8 (μ-dpmppm) 4 ](BF 4 ) 4 , to the vacant terminal sites of which neutral two-electron donor ligands such as isocyanides and coordinative solvent molecules were readily incorporated to form the terminal-capped [Pd 8 (μ-dpmppm) 4 (L) 2 ](BF 4 ) 4 (L = XylNC, CH 3 CN ( [4](BF 4 ) 4 ), N,N-dimethylformamide (dmf)). These Pd 8 chains exhibited interesting temperature-dependent thermochromics behaviors with near IR absorptions (∼900 nm) arising from a spin-allowed HOMO−LUMO transition.…”

Synthesis and structures of dinuclear RhIII and IrIII complexes supported by a tetraphosphine, meso- or rac-bis{[(diphenylphosphinomethyl)phenyl]phosphino]}methane

“…The flexible coordination behavior of mesodpmppm further organized stepwise assemblies of heterotrinuclear metal ions of [PdCl 2 (Cp*M 0 Cl 2 )(Cp*MCl 2 )(m-dpmppmk 2 ,k 1 ,k 1 )] and [PdCl(m-Cl)(Cp*M 0 Cl)(Cp*MCl 2 )(m-dpmppm-k 2 ,k 1 ,k 1 )] þ (M, M 0 ¼ Rh, Ir, Cp* ¼ h 5 -pentamethylcyclopentadienyl) [38]. In addition, we have recently been successful in establishing lowvalent octapalladium chains supported by meso-dpmppm, as a coordinatively unsaturated Pd 8 rod, [Pd 8 (m-dpmppm) 4 ](BF 4 ) 4 , and the terminal-capped [Pd 8 (m-dpmppm) 4 (L) 2 ](BF 4 ) 4 (L ¼ 2,6-xylyl isocyanide (XylNC), CH 3 CN, N,N-dimethylformamide (dmf)) [39,40]. These Pd 8 chains exhibited interesting temperaturedependent dynamic behaviors in the solution states.…”